Process for carbonylating alkanols

ABSTRACT

Controlled addition of olefins to alcohol carbonylation zone to prevent water build-up and sustain acidic liquid catalyst activity.

United States Patent Kwantes et a1.

[ 51 June 20, 1972 [54] PROCESS FOR CARBONYLATING ALKANOLS [72]lnventors: Arien Kwantes; Bernhard Stouthamer,

both of Amsterdam, Netherlands [30] Foreign Application Priority DataNov. 15, 1968 Great Britain ..54,33 H68 [52] [1.8. CI. ..260/4l3,260/532, 260/514 C [51] int. Cl ..C07c 51/12 [58] Field 01 Search..260/532, 533 A, 497 R, 413

[56] References Cited UNITED STATES PATENTS 2,986,577 5/1961 Kurhajec..260/532 X Loder 2,158,031 5/1939 Loder 260/532 X 2,217,650 10/1 940Loder ..260/532 2,739,169 3/1956 Hagemeyer FOREIGN PATENTS ORAPPLICATIONS 1,142,167 1/1963 Germany ..260/532 Paulis et a1..."

Pawlenko Primary Examiner-Lorraine A. Weinberger AssistantExaminer-Richard D. Kelly Attorney-John J. Colvin and E. Walter Mark [57] ABSTRACT Controlled addition of olefins to alcohol carbonylation zoneto prevent water build-up and sustain acidic liquid catalyst activi- 4Claims, 1 Drawing Figure PROCESS FOR CARBONYLATING ALKANOLS BACKGROUNDOF THE INVENTION It is known that monohydric alcohols are convened intocarboxylic acids, when caused to react with carbon monoxide in thepresence of a strongly acidic liquid catalyst. The carboxylic acidmainly formed is a monocarboxylic acid having one carbon atom permolecule more than the starting alcohol. Depending on the monohydricalcohol and acid involved, ester may be formed to a varying degree. Thisester formation generates water. In addition, a small quantity of wateris fonned when a minor quantity of monocarboxylic acids having a highermolecular weight than the desired acid formed. Although many of theacidic catalysts employed in this reaction contains minor amounts ofwater, major addition of water to the catalysts tends to reduce theiractivity unacceptably. Thus, in a continuous process, wherein thecatalyst is recirculated in the absence of water removal, the catalystwould become increasingly inactive by gradual dilution.

STATEMENT OF THE INVENTION It has now been found that undesirable waterbuild-up may be eliminated in the continuous production of a carboxylicacid and/or ester by reaction of a monohydric alcohol with carbonmonoxide by adding during the course of the process a suitable waterbinding or water removing material. In accordance with the inventionorganic acids and/or esters are produced with improved efficiency and inthe absence of any substantial water build-up by the steps comprising:

a. introducing into a reactor a highly acidic liquid catalyst, themonohydric alcohol to be converted and carbon monoxide,

b. dividing the liquid reactor effluent into a phase comprisingcarboxylic acid and/or ester and a phase comprising water-containinghighly acidic liquid catalyst,

c. recycling at least part of the highly acidic liquid catalyst I phaseto the reactor, and

d. introducing into the reactor a controlled amount of an olefin capableof reacting in the water under the conditions employed.

In a preferred aspect of the invention the olefin added is one whichunder the reaction conditions employed will react with both carbonmonoxide and water to form the desired carboxylicacid and/or ester.

The invention will be described hereinafter with reference to theaccompanying drawing, wherein the single figure illustrates more or lessdiagrammatically one form of apparatus suitable for carrying out theinvention.

WATER REMOVING OLEFIN Olefins used for water-removal in the process ofthe invention comprise the monoolefins, and monoolefin-containingmixtures, which upon reaction with carbon monoxide and water form theacid and/or ester corresponding to the desired alcohol carbonylationreaction product. Certain other olefins may similarly remove water;however, acids formed therefrom are generally contaminants which mustthen be separated from the desired product.

When a primary alcohol is charged the corresponding alpha olefin ispreferably used as the water removing compound. For example, pentene-lis used with pentanol- 1; both forming the secondary acid,2-methylpentanoic acid under the conditions employed.

Secondary alcohol starting materials generally result in thesubstitution of a carboxylic group for the hydroxyl group. For example,butanol-2 reacts with carbon monoxide to form 2- methyl butanoic acid.In the latter case either butenel or butene-2 is preferably used as thewater-removing olefin.

When a tertiary alcohol is used as starting material the resulting acidwill generally correspond to the substitution of a carboxylic group forthe hydroxyl group. For example, tertbutanol is converted with carbonmonoxide into trimethyl acetic acid. ln this case isobutylene is thepreferred waterremoving compound, the carbon monoxide adding to the morebranched olefinic carbon.

Olefins suitable as water-removing compound according to the inventioncomprise both monoolefins which under the reaction conditions applied donot undergo any substantial decomposition, and monoolefins which underthe conditions decompose partly or completely into lower olefins.Preference is given to olefins belonging to the latter group since theycan be stored as a liquid under atmospheric pressure at ambienttemperature. Examples of the latter group are diisobutene, triisobuteneand tetraisobutene; the first two being preferred. Olefins of this groupdecompose for the greater part into isobutene, which subsequently reactsrelatively rapidly with water and carbon monoxide under the conditionsemployed to form trimethyl acetic acid.

ALCOHOL CHARGE The organic charge reacted with carbon monoxide inaccordance with the invention comprises organic compounds containing onealiphatic carbinol group as the sole reactive group. Suitable organiccompounds comprise the alcohols represented by the empirical formula:

wherein R represents a hydrocarbyl group containing at least threecarbon atoms attached to the oxygen atom through an aliphatic carbonatom. R preferably represents a saturated hydrocarbon radical, eitheralkyl or cycloalkyl such as propyl, n-butyl, i-butyl, tert buytl, amyl,hexyl, heptyl, octyl, nonyl, decyl and corresponding cycloalkyls andhydrocarbonsustituted cycloalkyls. R most preferably represents asecondary or tertiary alkyl. Examples of alcohols of the abovedefinedclass are: n-propanol, n-butanol, tert-butanol, isopropanol,cyclohexanol, methylisobutyl carbinol, cyclohexanol, methylisobutylcarbinol, cyclopentyl carbinol, the normal, secondary and tertiaryhexanols, heptanols, octanols, nonanols and decanols. A suitable chargematerial comprises the alcoholic products of the OX0 synthesis. Alcoholshaving from three to twenty carbon atoms to the molecule constitutepreferred charge materials to the process. Of the suitable alcoholcharge materials, those having from three to 10 carbon atoms to themolecule wherein a hydroxyl group is directly attached to a secondary ortertiary carbon atom are particularly preferred, such as isopropanol,sec-butanol, tert butanol, secand ten hexanol, and the like. Mostpreferred are the tertiary alcohols of from three to 10 carbons.

As stated hereinbefore, alcohols are converted into acids and/or esters.Which product predominates depends in part upon the alcohol charged.Little or no esterification takes place when the acid is formed at ahigh reaction rate. However, when the acid is formed at a relatively lowrate, it is being formed in the presence of a relatively largeproportion of alcohol and therefore will more easily esterify.

When primary alcohols generally react relatively slowly and the acidformed is subsequently converted nearly entirely into the ester.Secondary alcohols react relatively fast with carbon monoxide under theconditions of the present process, so that only a relatively small partof the acid formed is converted into ester. Tertiary alcohols react veryfast with carbon monoxide, only acids and no esters being formed. Theprocess according to the invention is therefore particularly attractivefor converting tertiary butanol into trimethyl acetic acid, an importantstarting material for the preparation of a great variety of organiccompounds. Furthermore, the acids and/or esters are obtained in a highyield when the preferred secondary and tertiary alcohols are used.Mixtures of two or more of the abovedefined alcohols may be charged tothe process of the invention.

CARBON MONOXIDE REACTANT Preferably substantially pure carbon monoxideis used. The process according to the invention, however, is notrestricted as regards the source of the carbon monoxide-containing gasto be used. The carbon monoxide-containing gas may be any mixture ofcarbon monoxide with one or more inert gases, such as for examplehydrogen, nitrogen or gaseous alkanes. The carbon monoxide is preferablypresent in a gas containing at least 50 percent by volume of carbonmonoxide.

ACIDIC CATALYST A great variety of highly acidic liquid catalysts may beused in the process according to the invention. Suitable catalystscomprise orthophosphoric acid, sulfuric acid, chlorosulphonic acid, ormixtures thereof with boron trifluoride and water. The preferred liquidcatalyst is a liquid complex mixture of orthophosphoric acid, borontrifluoride and water. The reaction under the influence of this catalystis very rapid so long as the amount of water present is controlled. Sidereactions such as polymerizations hardly occur. In these preferredcatalysts, the molar ratio of H to BB, is suitably maintained betweenabout 1 to 1 and about 2.3 to 1, these ratios giving optimal catalyticactivity. Preferred are molar ratios of R 0 to BF between about 1 to land about2 to l with ratios between about 1.2 and l and about 2 to ibeing especially preferred. The molar ratio of BF to H PQ, is suitablymaintained between about 2 to l and about to l with ratio between about2 to l and about 10 to 1 being preferred. More preferred are molarratios of BB, to l-i PO of from about 2.5 to 1 about 6 to l with ratiosof from about 3 to l to about 4.5 to I being especially preferred.

REACTION CONDITIONS The process of the invention is preferably carriedout at a carbon monoxide partial pressure in the range of from about toabout 400 kg/cm and in particular in the range of from 50 to 200 kg/cmThe process is preferably carried out at a temperature in the range offrom 50 to 150 C, but temperatures outside the latter range may be usedas well. The desired carboxylic products are obtained in very high yieldwhen the process is carried out at a temperature in the range of from 75to 125 C.

The process may be carried out in any form of continuous reactor. Theyield of carboxylic acid and/or ester is favorably influenced when thereaction mixture is vigorously stirred. Therefore, the reactor ispreferably provided with a stirrer having a power input of at least 0.5hp per m The liquid reactor effluent usually consists of one liquidphase. Addition of an inert solvent for the carboxylic acid to thereaction mixture facilitates working up of the reactor effluent as iteffects a phase separation into a phase comprising carboxylic acidand/or ester and a phase comprising highly acidic liquid catalyst.Preferred inert solvents comprise saturated unbranched hydrocarbons, inparticular of those having five, six or sevencarbon atoms per molecule.Examples of such hydrocarbons are n-pentane, n-hexane, n-heptane,cyclopentane and cyclohexane and mixtures thereof. Examples of otherinert solvents are isobutane and 2,2-dimethyl butane.

Splitting up of the liquid reactor effluent may be carried out in anydesired manner. The effluent is preferably split up utilizing the phaseseparation which occurs when inert diluent is added as describedhereinbefore. Separation is then carried out, for example, in a settlingtank. The highly acidic liquid catalyst recovered by phase separation asan aqueous phase is preferably recycled quantitatively to the reactor.The carboxylic acid phase is preferably washed with water, thus removingwater-soluble compounds, particularly catalyst. For this washing anyknown technique and apparatus are in principle suitable. For example, astirred vessel may be used. The said washing procedure is preferablycarried out in a rotating disc contractor. The material to be washed andwater are preferably passed through the said contractor incountercurrent. The water used to wash the carboxylic acid phase may bepartly and is preferably quantitatively recycled to the reactor. The

water thus introduced into the reactor is easily removed by using acorrespondingly larger quantity of water-removing compound.

The washed material, consisting of carboxylic acids and.

inert diluent may be further purified by distillation of the inertdiluent overhead and separating the acids as a bottom product. Thisdistillation is preferably carried out at atmospheric or subatmosphericpressure, distilling at subatmospheric pressure having as an advantagethat decomposition of the carboxylic acids and/or esters being distilledis avoided. The acids thus purified can, if desired, be further purifledby one or more known techniques.

Referring to the drawing: as typical, the preparation of trimethylacetic from tertiary butanol, using n-pentane as solvent and diisobuteneas water-removing compound is described hereinafter.

Tertiary butanol and diisobutene are introduced via line 1 1 intoreactor 12. As solvent n-pentane is introduced into the reactor viavalved line 14, or preferably at least in part as recycle via valvedline 15. Carbon monoxide is supplied via line 16, and a recycle streamof a liquid complex mixture of phosphoric acid, boron trifluoride andwater is supplied via line 17 to reactor 12. Reactor 12 is provided witha mechanical stirrer 19. Liquid is withdrawn from reactor 12 via line 20and introduced into a settling tank, 21. In settling tank 21 an upperphase A consisting of a solution of trimethyl acetic acid in n-pentanecontaining a minor quantity of acids having more carbon atoms permolecule than trimethyl acetic acid, is separated and conducted via line22 to mixing vessel 24 equipped with stirrer 25, in which the crude acidis washed with water. This water is supplied to vessel 24 partly asmakeup water supplied via line 26 and partly as recycle via line 27. Themixed liquids are withdrawn from vessel 25 via line 29 and introducedinto a settling tank, 30, from which the upper phase C, which consistsof crude trimethyl acetic acid and npentane, is withdrawn via line 31and conducted into a fractionator 32. The bottom fraction withdrawn fromfractionator 32 via line 34 consists of crude trimethyl acetic acidwhich may be further purified, if desired, by means not shown.

The overhead fraction withdrawn from column 32 via line 15 consists ofn-pentane and may be removed via valved line 35 but preferably isintroduced into line 11, as mentioned hereinbefore. The lower phase Dobtained in settling tank 30 consists of wash water and is conducted,partly via lines 36 and 27 to vessel 24, as described hereinbefore, andpartly via line 36 either to valved line 37 for removal or preferably toline 17 for recycle to reactor 12. The lower phase B separated insettling tank 2] is recycled via line 17 to reactor 12 as describedhereinbefore. Make-up catalyst is added via valved line 39.

The amount of diisobutene supplied via line 1 l is sufficient to removethe water formed inside reactor 12 as well as the water introduced intothe reactor via line 17 The process of the invention is furtherillustrated by way of the following Example.

EXAMPLE In a continuous operation 400 g of liquid catalyst, 111 g oftertiary butanol, g of n-pentane and [9.8 g of diisobutene were fed perhour to a reactor having a volume of 1% liter made of Hastelloy C" (aregistered trade name), provided with 4 baffles and a double-bladepropeller stirrer. The catalyst consisted of ortho phosphoric acid,boron trifluoride and water in a molar ratio of l 4 6.5, respectively.The temperature of the reactor contents was maintained at 100 C, thecarbon monoxide pressure was 100 kglcm pure carbon monoxide being used.

The liquid leaving the reactor was separated into liquid catalyst anddilute acids, the latter phase was washed with water and subsequentlyn-pentane was distilled off from the washed dilute acids. The separatedliquid catalyst and the spent wash water were returned to the reactor.The acids were obtained in a quantity of 181 g/h, indicating that thetertiary butylalcohol and the diisobutene fed to the reactor were fullyconverted into acids.

The composition of the acids is presented in Table I.

TABLE I %w C acids 0.l trimethyl acetic acid 83.0 C -C acids 2.2 C acids13.6 C acids 1.!

The water balance of the material entering the reactor and the materialleaving the reactor was as follows:

The results of this experiment show that diisobutene is capable ofremoving water under the conditions prevailing in the reactor.

We claim as our invention:

1. In the process wherein, in a reaction mixture, an alkanol selectedfrom the group consisting of secondary and tertiary monohydric alkanolshaving from 3 to 20 carbon atoms is continuously contacted in liquidphase with carbon monoxide in the presence of an aqueous catalystcomprising a mixture of H PO BB, and water, in which catalyst the molarratio of BF}, to l-l PQ, has a value between about 2 to l and about 20to l and the molar ratio of water to BE, has a value between about 1 tol and about 2.3 to l, the improvement consisting essentially of (a)effecting the contacting at a temperature in the range of from about 50C to about l50 C, while maintaining the molar ratio of water to BE, inthe defined range by the controlled addition of a monoolefinicallyunsaturated hydrocarbon having from 3 to 20 carbon atoms to the reactionmixture and (b) continuously removing the resulting carboxylicacid-containing mixture and separating into an organic phase consistingessentially of carboxylic acid and unreacted alkanol and an aqueouscatalyst phase and (c) returning said aqueous catalyst phase to thereaction mixture.

2. The process in accordance with claim 1 wherein said alkanol issecondary or tertiary alkanol having from about 3 to about 10 carbonatoms and said monoolefinically unsaturated hydrocarbon comprises amajor proportion of an olefin having from 3 to 10 carbon atoms.

3. The process in accordance with claim 2 wherein said alkanol isisobutanol and said monoolefinically unsaturated hydrocarbon is selectedfrom the group consisting of isobutene, diisobutene, triisobutene andtetraisobutene.

4. The process in accordance with claim 1 wherein an inert solventcomprising saturated unbranched hydrocarbons having from about 5 toabout 7 carbon atoms per molecule is added to the reaction mixture.

2. The process in accordance with claim 1 wherein said alkanol issecondary or tertiary alkanol having from about 3 to about 10 carbonatoms and said monoolefinically unsaturated hydrocarbon comprises amajor proportion of an olefin having from 3 to 10 carbon atoms.
 3. Theprocess in accordance with claim 2 wherein said alkanol is isobutanoland said monoolefinically unsaturated hydrocarbon is selected from thegrOup consisting of isobutene, diisobutene, triisobutene andtetraisobutene.
 4. The process in accordance with claim 1 wherein aninert solvent comprising saturated unbranched hydrocarbons having fromabout 5 to about 7 carbon atoms per molecule is added to the reactionmixture.